1. Field of the Invention
This invention relates to an analytical method for determining a particular component in a fluid sample based on optical change, such as, colorimetry. More particularly, this invention relates to a method for shortening of analysis time in such an analytical method.
2. Description of the Prior Art
Colorimetric analysis is a method based on optical change, such as, coloring or color change, caused by the reaction of a suitable reagent with the object substance to be detected (analyte). In a conventional analysis using a chemical reaction in solution, a reagent which reacts with the analyte to produce an optical change is added to the sample solution. On the other hand, in the dry method recently developed, the liquid sample is spotted on an analytical element containing the reagent, and the optical change occurring in the element is measured. Examples of dry-type analytical elements are disclosed in U.S. Pat. No. 3,992,158, U.S. Pat. No. 4,292,272, etc.
As described above, when a reagent is added to a sample solution, or when a sample solution is spotted on a dry-type analytical element, the analyte in the sample reacts with the reagent to produce coloring or the like. For example, when a blood sample or a blood plasma sample is spotted on the dry-type analytical element described in U.S. Pat. No. 4,292,272, glucose in the sample reacts with the reagent to form a colored substance, such as, a red colored substance. The optical density of the dry-type analytical element corresponds to the amount of the colored substance produced. Therefore, the reflection optical density is measured after a prescribed time, and it is converted to glucose concentration (blood sugar value) by using a calibration curve obtained previously. In the wet method, transparent optical density is usually measured.
In the prior art, measurement of optical density has been measured only once after a prescribed time from the spotting of a sample solution or the addition of the reagent, except for a rate assay for determining enzyme activity or the like. However, in the case of a lower analyte concentration, the reaction finishes in a relatively short period, and it is generally not necessary to wait till the above prescribed time. On the other hand, for higher analyte concentrations, the analytical accuracy is lowered if the reaction time is short, because the slope of the calibration curve is small for such a case and thus the variation coefficient of the determined concentration increases.